The present subject matter relates to internal combustion engine diagnostics and more specifically to apparatuses and methods for determining the spatial and temporal nonuniformities of CO2 in a complex fluid stream. A complex fluid stream may contain concentrations of CO2 that vary with space, time and temperature.
Internal combustion engines typically suffer from the production of undesirable NOx emissions. Experience has revealed that more NOx emissions are formed at higher combustion temperatures and that NOx formation has a nonlinear dependence on temperature. More specifically, lowering the combustion temperature by small amounts can result in relatively large reductions in NOx formation and is favorable in that respect.
Exhaust-gas recirculation, EGR, is a known technology used to reduce automotive NOx emissions, and involves mixing some of the engine exhaust gas products with the intake air stream before it enters the combustion chamber. The exhaust products act as a diluent in the inlet air that reduces peak combustion temperature. Ideally, the air/exhaust mixture, or EGR fraction, is uniform across the various cylinders of a multi-cylinder engine. However, practically, the EGR fraction can vary from cylinder to cylinder and cycle to cycle due to various spatial and temporal nonuniformities; e.g., non-ideal mixing characteristics, intake-manifold restrictions and path length differences, and overlap of valve timing events with manifold resonating. The actual combustion chamber charge is affected by: external EGR, residual backflow caused by valve overlap, and residual exhaust remaining in the combustion chamber between the piston and the cylinder head. Such nonuniformities can cause one cylinder to reach a limit (e.g., incomplete combustion, etc.) earlier than the other cylinders, and can limit the performance of the other cylinders. Ultimately, the result is lost efficiency and increased engine emissions.
Application Ser. No. 14/051,788, entitled EGR DISTRIBUTION AND FLUCTUATION PROBE BASED ON CO2 MEASUREMENTS describes an apparatus and method of determining spatial and temporal nonuniformities of CO2 in an intake stream.
CO2 absorption spectra are affected by the temperature of the intake fluid stream itself. Since the backflow exhaust portion will be at a higher temperature than the external EGR, temperature correction is necessary to ensure CO2 measurement is not underestimated at higher temperatures. See FIG. 1-3 for an illustration of these known phenomena.
Water vapor concentration may be used to determine intake charge temperature in the regions of CO2 measurements for correction and more accurate measurements.
Jatana G S, Naik S V, Shaver G M, Lucht R P. “High-speed diode laser measurements of temperature and water vapor concentration in the intake manifold of a diesel engine.” International Journal of Engine Research October 2014 vol. 15 no. 7 773-788 describes the use of a diode laser and absorption spectroscopy to determine the concentration of water vapor in an intake stream.
Jatana G S, Magee M, Fain D, Sameer V, Shaver G M, Lucht R P. “Simultaneous high-speed gas property measurements at the exhaust gas recirculation cooler exit and at the turbocharger inlet of a multicylinder diesel engine using diode-laser-absorption spectroscopy.” Applied Optics, vol. 54, issue 5, p. 1220 describes the use of a diode laser and absorption spectroscopy to determine temperature, pressure and H2O vapor concentrations. See FIG. 3 for an example of known H2O vapor concentration spectra at two temperatures.
What is needed is an apparatus and method for measuring spatial and temporal CO2 concentrations in a complex fluid stream that includes relatively cool external EGR and relatively hot backflow exhaust species present.